[CQ-Contest] band-pass filtering -- a new approach?

Guy Olinger, K2AV k2av at contesting.com
Fri Nov 9 12:10:26 EST 2001

The lack of filtering the transmitted signal will bother you quite a bit,
and I would respectfully propose that this disadvantage will greatly
outweigh a
hundred watts on the output. Eg, a fraction of a db versus wiping out weak
received signals on SO2R

At NY4A CQWWCW multi this year, I'm going to add a HIGH POWER filter after
the amp on 40m
to cut down on the interference to 15. Probably could do the same with
*properly* installed stubs, but that is the rub, getting that right, so will
cheat by spending some money for the high power 40m bandpass.

By any angle I can think of, SO2R invokes all the cross interference
problems of multi-multi except nX +- nY intermod, and except you only annoy
yourself, and maybe that's
worse. I'm betting there's no way you can cheat or finess the problem.

GL & 73, Guy.

----- Original Message -----
From: "Pete Smith" <n4zr at contesting.com>
To: <cq-contest at contesting.com>
Sent: Friday, November 09, 2001 10:12 AM
Subject: [CQ-Contest] band-pass filtering -- a new approach?

> I've been researching band-pass filtering for SO2R, and it has occurred to
> me to try a different approach if the peer review sounds favorable.
> What I'm planning is to build a box for each of my transceivers,
> a receiver protection circuit (diodes and a resistor), receive-level
> bandpass filters and a relay switching matrix to select the filters AND
> bypass them on transmit.  This would seem to offer several advantages --
> I can use W3LPL's 3-pole receive filter circuit, which uses standard cap
> values and delivers performance that is probably superior to any
> alternative except for W3NQN's expensive transmit filters.
> I avoid issues with burning out the filter components from transmit power,
> particularly with a messy amplifier input SWR on some bands.
> I avoid the reduction in drive to my SB-220, which really needs its 120
> I can be fairly relaxed about the physical layout, since SWR is not the
> issue it is on the transmit side.
> I realize that having a bandpass filter on the transmit side offers
> advantages too, in particular reducing harmonic output and wideband noise.
> But on balance, this seems like a good idea, plus it'll give me a project
> for the winter.  Comments?
> 73, Pete N4ZR
> www.qsl.net/n4zr
> --
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